chapter 8 natural selection: empirical studies in the wild
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Chapter 8 Natural selection: empirical studies in the wild. Diversity in Darwin’s finches. Medium ground finch. Variation in beak size influences efficiency at eating different types of seeds. Beak size evolution. Drought resulted in more hard, woody seeds Favored larger beaked birds. - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 8Natural selection: empirical
studies in the wild
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Diversity in Darwin’s finches
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Medium ground finch
• Variation in beak size influences efficiency at eating different types of seeds
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Beak size evolution
• Drought resulted in more hard, woody seeds– Favored larger beaked
birds
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Natural selection is variable over time
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Key Concepts
• Beak size influences fitness and is heritable– Natural selection can cause change
• Directional selection favors increases or decreases in the mean of a trait
• Stabilizing selection favors average values of a trait
• Long-term studies reveal fluctuation in the direction and strength of natural selection
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Coat color variation affects fitness
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Light coat color evolved independently in different populations
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Key Concepts
• Evolution in response to natural selection is inevitable if:– There is variation in a trait– Variation is heritable– Some variants reproduce more than others
• Specific features of the environment can generate natural selection on a trait
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Natural selection can be variable across space
• Gene flow can bring alleles to new locations– Alleles may increase or decrease fitness
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Aposematism favored only in areas where coral snakes co-occur
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Key Concepts
• Natural selection can lead variation over the geographic range of a species
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Gall flies induce plants to produce galls
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Gall diameter is variable and heritable
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Stabilizing selection on gall size
Intermediate size favored
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Key Concepts
• Stabilizing selection results when agents of selection act in opposing directions
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Eda gene involved in production of lateral plates in stickleback
Marine ancestral form
Freshwater derived form
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Shift in dorsal spine length recorded in fossil record
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Low Eda allele favored in freshwater populations
• Production of armor energetically costly – Little predation pressure to counterbalance
• Low Eda allele present at low frequency in marine environment– Favored when introduced to freshwater
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Ability to digest lactose as adults found in certain populations
- Lactase expression persists into adulthood
- Correlates with domestication of cattle
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Strong evidence for positive selection on lactase persistence alleles
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Artificial selection in crop production
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Artificial selection in crop production
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Gradual increase in cob size documented by archaeologists
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Domestic dog diversity created in last 15,000 years
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Pesticides and herbicides act as agents of selection
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Resistance to pesticides in houseflies
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Rapid evolution of herbicide resistance
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Alteration in EPSPS enzyme leads to Roundup resistance
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Creation of refuges can slow the evolution of resistance
• Bt crops select for resistance in pests– Comes at a cost when Bt is not present
• Creation of Bt-free refuges favors Bt-susceptible insects– Slows evolution of resistance
• Refuges are now required by law
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Introduced cane toads have led to evolution of black snake populations
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Evolution of shorter male horns due to hunting
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Cod fishing has influenced life-history evolution
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Key Concepts
• The speed of evolution depends on amount of genetic variation and strength of selection– Leads to rapid resistance in pest populations
• An understanding of evolutionary biology can lead to novel management practices